In the present study, we found that pyridostigmine reduced hypertension, restored the autonomic balance by inhibiting sympathetic hyperactivity and enhancing vagal activity, reduced oxidative stress and the inflammatory response, and suppressed RAS activation in PVN in hypertensive rats (Fig. 9).
Hypertension is a blood pressure elevation and it can directly damage multiple organs [21]. A decrease in blood pressure is protective and reduces the incidence of cardiovascular events [22, 23]. Lataro et al. found that cardiovascular dysfunction was observed in spontaneously hypertensive rats. Acetylcholinesterase inhibitors reduced hypertension and improved cardiovascular function in hypertensive rats [24]. Similarly, our result showed that 2K1C rats exhibited elevated blood pressure and cardiovascular dysfunction. Treatment with pyridostigmine significantly reduced blood pressure and improved cardiac and vascular functions. Therefore, the protective effects of pyridostigmine on the heart and blood vessels may be attributable to the fact that pyridostigmine decreases blood pressure.
Compelling evidence indicates that hypertension is associated with an autonomic imbalance characterized by enhanced sympathetic activity and reduced vagal activity [25–27]. Pharmacological inhibition of the former activity is thus useful [28, 29]. Rocha et al. reported significant increases in sympathetic activity in certain animal models of cardiac dysfunction, while treatment with pyridostigmine had cardioprotective effects by suppressing sympathetic activity [17]. Consistent with their studies, we found that sympathetic activity was elevated in 2K1C rats and that pyridostigmine reduced this activity and attenuated hypertension. On the other hand, pyridostigmine directly decreases blood pressure by improving vagal activity in spontaneously hypertensive rats [30]. Cavalcante et al. found that rats with L-NAME-induced hypertension exhibited a significant reduction in vagal tone and that pyridostigmine increased vagal activity and prevented hypertension [31]. In line with their study, our results showed that vagal activity decreased in 2K1C rats and that pyridostigmine enhanced vagal tone and reduced hypertension. Therefore, pyridostigmine may attenuate hypertension by restoring the autonomic balance between the sympathetic and vagal nervous systems.
There is convincing evidence indicates that the inflammatory response and oxidative stress together affect the SFO-PVN-RVLM pathway that regulates blood pressure [32, 33]. Increased levels of pro-inflammatory cytokines accompanied by decreased levels of anti-inflammatory cytokines in the SFO, PVN, and RVLM are observed in hypertensive animals. Restoration of the balance between pro- and anti-inflammatory cytokines at any point of the pathway attenuates hypertension [34]. A recent study found that plasma IL-6 and TNF-α levels were significantly increased in spontaneously hypertensive rats and that acetylcholinesterase inhibition decreased the pro-inflammatory cytokine levels and the blood pressure [35]. Meanwhile, some study showed that the development of hypertension was associated with the decreased IL-10 level [36]. IL-10 supplementation increases Treg cell numbers and attenuates hypertension in RUPP rats [37]. Consistent with their studies, we found that IL-6 and TNF-α levels increased and that IL-10 level decreased in 2K1C rats. Treatment with pyridostigmine decreased the levels of pro-inflammatory cytokines and increased the level of anti-inflammatory cytokine and attenuated hypertension. In addition, ROS synthesized by NADPH oxidase increases the neural traffic of the SFO-PVN-RVLM axis in hypertensive animals and a reduction in the ROS level at any point of the pathway attenuates hypertension [38]. Yang et al. found that animals exhibiting sympathetic hyperactivity developed myocardial oxidative stress injury and that pyridostigmine had cardioprotective effects by decreasing such injury [39]. In agreement with their study, we found that the PVN levels of ROS, NOX-2, and MDA increased and that of SOD decreased in hypertensive rats. Pyridostigmine inhibited PVN oxidative stress injury and attenuated hypertension. In summary, pyridostigmine may attenuate hypertension by decreasing the PVN inflammatory response and oxidative stress.
RAS activation is one of the most important causes leading to oxidative stress and inflammatory response in PVN in the development of hypertension [40]. Inhibition of PVN RAS activation has anti-hypertensive effects [41]. Recent studies have reported increased ACE, Ang II, and AT1R levels in hypertensive rats and that exercise decreases those levels and attenuates hypertension [42]. In agreement with their study, we found that PVN RAS was activated, as evidenced by increased ACE, Ang II, and AT1R levels, in 2K1C rats. Pyridostigmine decreased these levels and attenuated hypertension. Thus, pyridostigmine may directly inhibit PVN RAS activation by reducing the levels of the principal RAS components, and anti-hypertension. Meanwhile, we found that the PVN AT2R level was decreased in 2K1C rats and pyridostigmine increased that level. A recent study found that AT2R countered the detrimental effects of AT1R, and inhibited ACE [43]. Therefore, pyridostigmine may also suppress the effects of AT1R in PVN by increasing AT2R level and attenuate hypertension. Notably, we found that pyridostigmine had no significant effect on the plasma level of Ang II in any group. The level was elevated in week 1 but not in week 4 in 2K1C rats [44]. Hence, plasma Ang II almost returned to normal level in hypertensive rats at eighth week and the effect of pyridostigmine on plasma Ang II was not significantly observed in the present study.
In conclusion, we found that PVN RAS-mediated oxidative stress and inflammation increased sympathetic outflow and ultimately hypertension. Pyridostigmine inhibited PVN RAS activation, suppressed PVN oxidative stress and inflammation, restored the balance between the sympathetic and vagal nervous systems, and ameliorated hypertension. Pyridostigmine may be useful for treating hypertension-related cardiovascular diseases.